A week has gone by, and it is still lingeringly glad morning. Within and outside America, there is widespread delight at the imminent departure of George Bush, but also on account of very much more. Across the continents, the prospect of a charismatic and highly intelligent president who is at once biracial and cosmopolitan has revived belief in the US as the quintessential land of opportunity; while in America itself, the election of Barack Obama is also seen as a kind of absolution and partial atonement for centuries of black slave suffering, mob lynchings and segregation.

In global historical terms, too, his election constitutes in some respects a revolution. Not since Suleiman the Magnificent in the 16th century, has anyone not "white" possessed anything like the degree of trans-continental power that will soon be exercised by President Obama. So striking is his victory that it can obscure other respects in which these US elections broke the mould.

For the first time in history there was a female candidate in the race for the presidency, Hillary Clinton, who possessed a real chance of winning (and might have had it not been for the Obama phenomenon). Moreover, for the first time since Geraldine Ferraro ran in 1984, another woman, Sarah Palin, was picked as a candidate for the vice-presidency. Also notable was a partial blow against ageism. Had John McCain won, he would have become president at the age of 72.

To appreciate the diversity on show in this campaign, one has only to glance at the state of British politics. Benjamin Disraeli, Margaret Thatcher, and John Major were able to become prime minister despite the obstacles of being, respectively, Jewish by birth, female, and minus a university degree - but at present the Westminster system does not appear strikingly productive of diversity at the very top. No UK party seems to possess a non-white MP of Obama's calibre. Post-Thatcher, the female candidates who have stood in leadership elections for the three main political parties have been dismally few in number and not overwhelming in talent; and if the Conservatives win the next general election, the proportion of women in the Commons, like the proportion of non-whites, will almost certainly decline.

Moreover, the forcing out of Menzies Campbell as Liberal leader, at least in part on account of his age, compares poorly with the Republican espousal of McCain and Ronald Reagan. Whether Labour, Liberal or Conservative (or indeed SNP or Plaid Cymru), Britain's current party leaders are without exception middle aged, middle to upper class, white and male.

Does this mean that America's political system and voters are more open and welcoming to difference of all kinds? Only up to a point.

Hillary Clinton is tough, clever and formidably well briefed, and has been politically ambitious all her adult life. It is unclear however that she would have got as far as she did without her husband's name and contacts (while being simultaneously criticised on his account). Gender also underscores the limits of American anti-ageism. Reagan and McCain were able to exploit what may be called the Gandalf syndrome whereby elderly males can be viewed as wise and experienced - and therefore powerful. But can one really imagine the Democrats or Republicans (never mind a British party) selecting as leader a woman in her late 60s or early 70s? By the same token, as Gloria Steinem has pointed out, is it likely that a woman possessed of Barack Obama's CV - a mixed-race background, time as a community organiser, a legal qualification, two young children, and eight years as a state legislator - would have been chosen for the Senate? And would, say, a Barbara Obama, after just one term as senator, have then stood a chance of being elected to the Oval Office?

Then there is the matter of class and connections. The myth that virtually everyone in America is middle class was much rehearsed in these elections. In reality, the US possesses a powerful upper class, and one of the narrow gateways to it is still an Ivy League education (or alternatively passage through a top army or naval college, as in McCain's case). Obama and Bush have little in common, but each went not just to one, but two Ivy League universities; Michelle Obama is also Ivy League (Princeton); Hillary and Bill met when they were both at Yale; and so on and so on.

It might be argued that this illustrates American meritocracy, except it is not quite as simple as that. Both Obamas probably benefited to a degree from affirmative action, but the competition to get into Ivy League schools is so intense that success is always something of a lottery. Had Barack Obama been obliged to take his degree at the University of Akron, say, it is doubtful that his progress would have been remotely as stellar. As it was, he won early admission to the company and leverage of the influential, and now has the pleasure of deciding whether to appoint to his cabinet Lawrence Summers - who was president of one of Barack's alma maters, Harvard University.

It is partly this background of glittering prizes, I suspect, that accounts for some of the ferocity of Sarah Palin's attacks on Obama during the campaign. For while she may be "white", she is also in some respects far more of an outsider than he: not only female and not Ivy League, but also stuck in the wrong part of the US. As senator for Illinois, Obama could exploit one of the great traditional Democratic power bases, the city of Chicago, where he lives in one of the most fashionable and expensive districts. But Palin has to make do with distant, snowy Alaska, where four-legged creatures, despite all her efforts, outnumber humans. One of the reasons why the personnel of US politics are more diverse, is that - unlike the UK - one can compete for the top job without spending long years, or any years, in the nation's legislature. Being governor of Alaska allowed Palin the brief chance of a place at the top table: but it is not a location that makes high political achievement easy.

None of this means that Obama will necessarily be a less than radical president. Historically, individuals possessed of the confidence that privilege and good fortune bestow have often proved conspicuous reformers: think only of Franklin D. Roosevelt. But it is important to recognise that Obama is less an outsider than he appears. And one should not be surprised if some of his responses in office turn out to be more conservative than some of his euphoric supporters now expect.